Chapter 9: Central Nervous System Flashcards
1
Q
two divisions of the nervous system
A
1) central nervous system
- brain and spinal cord
- is the integrating centre
2) peripheral nervous system
- all neural tissue outside of the CNS
2
Q
what are neurons?
A
neurons are cells that send and receive electrical signals rapidly
3
Q
role of central nervous system
A
- consists of the spinal cord and the brain
- integrates information from internal/external environment to illicit appropriate responses for the maintenance of homeostasis
4
Q
role of peripheral nervous system
A
- includes all neural tissue outside the CNS
- provides communication between the CNS and the rest of the body
- has two divisions: somatic and autonomic
5
Q
What is CSF and why is it important?
A
- cerebrospinal fluid is a clear watery fluid that bathes the brain and spinal cord (the CNS)
- it is important because it helps with protection, nourishment, and waste removal in the brain
6
Q
main functions of CSF
A
- CSF cushions the brain (acts as a shock absorber) by preventing the soft nervous tissue from colliding with the hard skull
- CSF helps maintains a stable interstitial fluid environment because it provides neurons and glial cells with essential nutrients and helps with removal of waste products
7
Q
where does CSF come from?
A
- it is secreted by the ependymal cells of the ventricles in brain
- CSF is then circulated throughout the four ventricles
8
Q
how much blood supply is sent to the brain? why so much?
A
- the CNS receives 15% of the blood that the heart pumps
- a large blood supply is necessary because the CNS tissue has a high rate of metabolic activity compared to most other body tissues
- therefore, it has a high demand for glucose and oxygen to meet its energy needs
9
Q
what happens if there inadequate blood flow to the brain?
A
- can result in irreversible damage to CNS tissue
- can cause deficits in certain functions like the ability to speak or move an arm
10
Q
why is blood flow to the brain critical?
A
- to help meet the brains energy requirements
- blood flow provides oxygen and glucose to the brain which is needed needs to function properly and stay alive
- neurons in CNS depend on aerobic glycolysis (which requires oxygen and glucose) to maintain ATP levels therefore requiring a steady supply from the blood
11
Q
what are the different energy supplies to the brain?
A
- GLUCOSE and oxygen are the main energy supply
- ketones can be used for energy during extreme conditions when glucose supply is limited
12
Q
why is the CNS so sensitive to changes in blood supply?
A
it is because the brain and spinal cord have high metabolic demands and limited energy reserves.
- the brain has limited glycogen stores so cells in the CNS must obtain glucose directly from the blood instead
- cells in the CNS do not have access to fatty acids reserves for energy, which increases their demand for glucose
- neurons are more sensitive to oxygen deprivation than other kinds of cells with lower rates of metabolism (because they cannot perform anaeorbic glycolysis)
13
Q
what are capillaries?
A
- they are the site of exchange between blood and interstitial fluid
- they’re composed of a thin, single layer of endothelial cells (a type of epithelial cell)
- small wall = short diffusion distance for exchange
14
Q
what is blood-brain barrier?
A
- a physical barrier that is selectively permeable
- the capillaries in the brain create protective barrier that restricts the exchange of solutes between blood and brain
15
Q
how does the blood brain barrier work?
A
- barrier is the result of tight junctions between capillary endothelial cells
- they eliminate capillary pores which restricts the diffusion of molecules between the cells
16
Q
why are astrocytes important to the formation of the blood-brain barrier?
A
- they stimulate endothelial by releasing chemical signals that promote the formation of tight junctions between the endothelial cells of the brain’s blood vessels
17
Q
importance of the blood-brain barrier
A
- protects the CNS from harmful substances that may be present in the blood by restricting movement of molecules from the blood stream to the brain
- in order to move across the barrier (enter or leave capillaries) the molecules must cross the endothelial cells themselves.
18
Q
what is the spinal cord?
A
- a cylinder of nervous tissue
- is continuous with the lower end of the brain and is surrounded by the vertebral column
- is the origin of spinal nerves (31 pairs)
19
Q
what is organization of white and gray matter in the spinal cord?
A
gray matter = concentrated within a butterfly-shaped region in the middle of the cord
white matter = found in the surrounding outer region
20
Q
what is organization and role of gray matter in the spinal cord?
A
- divided into dorsal (posterior) and ventral (anterior) regions
- dorsal region = sensory functions / afferent
–> afferent neurons originate in the periphery as sensory receptors and terminate in the dorsal horn - ventral region = motor functions / efferent
–> efferent neurons originate in the ventral horn and travel to the periphery, where they form synapses with skeletal muscles
21
Q
what is organization and role of white matter in the spinal cord?
A
- white matter of the spinal cord form tracts that provide communication between the brain and spinal cord
–> ascending tracts = transmit information from spinal cord to brain
–> descending tracts = transmit information from brain to spinal cord
22
Q
what is a reflex?
A
an automatic, patterned response to a sensory stimulus
23
Q
what is a reflex arc?
A
- a neural pathways for reflexes
24
Q
3 reflex pathways
A
1) stretch reflex (i.e knee jerk)
2) withdrawal reflex
3) crossed-extensor Reflexes
25
5 components of a reflex arc
1) sensory receptor
2) an afferent neuron
3) integrating centre
4) an efferent neuron
5) an effector organ
26
how does the reflex arc work?
- the receptor first detects a stimulus
- information is then transmitted from the receptor to the CNS via the afferent neuron
- the CNS, which functions as the integrator, sends signals via the efferent neuron
- the efferent neuron transmits signals to the effector organ which stimulates it to produce a specific response.
-->the integration can consist of a single neuron or a network of neurons
27
4 classifications of reflexes
1) spinal or cranial
--> based on the level of neural processing involved
2) somatic or autonomic
--> depends on which efferent division controls the pathway
3) innate or conditioned
--> whether you're born with the reflex or learned through experiences
4) monosynaptic or polysynaptic
--> monosynaptic reflexes = the neural pathway consists of only two neurons and a single synapse
--> polysynaptic reflexes = contain more than two neurons and multiple synapses
28
what is the muscle spindle stretch reflex?
a rapid and automatic response to changes in muscle length
29
how does the stretch reflex work using the knee-jerk test?
- tapping the patellar tendon below the kneecap stretches the quadricep muscle. this causes a change in muscle fibre length.
- muscle spindles (which are sensory receptors) the muscle detect a change and get excited
- this triggers action potentials to travel in afferent neurons to the spinal cord (acting as an integration center)
- in the spinal cord, the afferent neurons make direct excitatory synaptic connections with efferent neurons that innervate the quadriceps muscle
- this stimulates the quadriceps to contract and the leg to “kick” forward
- the afferent neurons also synapse with inhibitory interneurons that innervate hamstring motor neurons allowing it to relax
30
what is a withdrawal reflex?
when a portion of the body is subjected to a painful stimulus, it withdraws from the stimulus automatically
31
what is the crossed-extensor reflex?
a contralateral reflex, meaning the reflex occurs on the opposite side of the body from the stimulus
32
how does the withdrawal reflex work?
- begins when specialized sensory receptors, such as pain receptors (nociceptors) in the skin, detect a harmful or painful stimulus
- the sensory/ afferent neurons transmit signals from the site of the stimulus to the spinal cord (integrating centre).
- the sensory/ afferent neurons enter the spinal cord and have an excitatory synapse with interneurons.
- the interneurons in the spinal cord excite and relay signals to the motor/efferent neurons that innervate the skeletal muscles that cause withdrawal of the limb
- these motor neurons stimulate the contraction in the affected limb.
- the contraction pulls the limb away from the harmful stimulus, allowing for a rapid and protective withdrawal.
- to facilitate the withdrawal, there is often a simultaneous relaxation of antagonistic muscles (those opposing the action), allowing for a quick and coordinated movement.
33
how does the crossed-extensor reflex work?
- begins with the detection of a painful stimulus in one limb which activates pain receptors (nociceptors) in the affected area
- sensory/ afferent neurons carry the pain signals from the stimulated limb to the spinal cord (integrating centre) where they synapse with interneurons.
- the interneurons have branches that can relay signals to motor/efferent neurons on both sides of the spinal cord which creates a coordinated response involving both the stimulated and opposite limbs.
- on the side where the painful stimulus occurs, motor/efferent neurons signal the muscles to contract (withdrawal reflex). This causes the withdrawal of the limb from the stimulus.
- simultaneously, on the opposite side of the body, motor/efferent neurons stimulate muscles to extend which helps support the body's weight and maintain balance during the withdrawal of the other limb.
